This invention relates to an apparatus for the application of an adhesive tape, longitudinally and with U-shaped cross section, about the edge of a shaped part of sheet metal, which apparatus is provided with tape-guiding means, comprising conveying rollers, and means for pre-folding the adhesive tape from which the pre-folded tape runs between two application rollers spring-biassed against each other which are adapted to press the tape simultaneously on to both sides of a shaped sheet metal part which is introduced into the tape-folding zone.
In the sheet metal processing industry the pasting over of metal parts-connecting folded seams by means of pressure or heat-hardenable adhesives is widely used. Thus, it is customary, for instance, in the automobile industry to seal in this manner folded seams of certain automobile body parts, in particular doors, and thereby to avoid the danger of corrosion.
In the automobile industry and similar branches of industry, there are usually employed adhesives in liquid or pasty form for producing such pasted-over folded seam joints, which adhesives are applied to the sheet metal parts to be joined in the form of a cord. This method of applying adhesive is unsatisfactory in several respects. One such drawback is seen in the fact that the distribution of the adhesive, attained by this method, over the entire folded seam is not sufficiently uniform, which fact may cause problems of corrosion, and, as another drawback, the use of adhesives in liquid or pasty form always causes problems of work hygiene.
In the manufacture of cans for preserving food and the like, it is also conventional to paste over folded seams or seal them with adhesives, as described, for instance, in U.S. Pat. No. 3,125,056, French patent application Publication No. 2,252,147 or Belgian Pat. No. 444,014. The adhesive is applied in these cases to the crimped edges of the parts of the can body to be connected with one another, either in liquid or pasty form, by extrusion or the like, or in the form of a strip of adhesive tape.
Adhesives in the shape of foils or, in particular, of tapes such as they are known by the trade names Araldit.RTM. and Redux.RTM. Adhesive Foil (CIBA-GEIGY) are increasingly used, especially because of their advantages of greater work hygiene. However, in the past, such adhesive foils or tapes have only found very limited use, or no use at all, for sealing or pasting-over folded seams, e.g., of automobile body parts.
This is preponderantly due to the fact that these adhesive films are highly cohesively plastic (of high viscosity) and that their low tensile strength causes considerable difficulties in applying them by machine operations. Additional complications arise when such adhesive strips must be applied to parts of automobile bodies whose folded seams have a complicated configuration, in particular one that is curved tridimensionally. These difficulties are especially great when a crimped rim is to be provided with adhesive on both sides thereof, i.e. when the adhesive tape is to be laid about the rim with a U-shaped tape cross-section.
The hitherto known apparatus of the initially described type are only suitable for processing relatively stiff adhesive tapes of considerable tensile strength (not self-adhesive films). This is, for instance, true of an apparatus described in U.S. Pat. No. 4,155,798 which comprises a pre-folding channel and press-on rollers.
In recognition of the fact that the lack of suitability of the known apparatus for applying cohesively plastic adhesive tapes of low inherent rigidity and tensile strength to curved metal sheet edges is caused above all by the rigid arrangement of the pre-folding channel and of the press-on or application rollers, and moreover by the fact that the application rollers are free-wheeling rollers (U.S. Pat. No. 4,155,798), an arrangement has already been proposed (European Pat. No. 72,779) in which, firstly, the pair of application rollers is pivotable as a unit about a common axis which extends parallel with the roller axes and spacedly ahead of them relative to the direction of tape conveyance, approximately in the plane of symmetry of the pre-folding channel, and in which, secondly, the application rollers can be motor-driven via elastically twistable shafts.
This arrangement constitutes a tremendous improvement over the known state of the art; however, extensive tests, carried out in practice, have shown that the quality of application could still be decisively improved in particular at higher speeds of application.